This invention relates to fluid supply apparatus and more particularly to such an apparatus which will take fluid from multiple fluid supplies in which the fluid exists at above atmospheric pressure, commingle the fluids in selected proportion, and supply the commingled fluids to a fluid user at a subatmospheric pressure.
Vacuum operated valves which use a vacuum control signal to a diaphragm to operate the valve have been known for some time, such as disclosed in U.S. Pat. No. 1,461,662 issued to Kawamura, U.S. Pat. No. 1,587,176 issued to Olsen, and U.S. Pat. No. 4,350,136 issued to Yanagisawa. Vacuum control valves which control the supply of a vacuum from a vacuum source to a vacuum user have also been known for some time, such as disclosed in U.S. Pat. No. 2,883,998 issued to Broughton. The known vacuum operated and vacuum control valves have shortcomings in that they will not take fluid from a fluid supply existing at a pressure of up to 100 pounds per square inch above atmospheric pressure and greater and reduce the fluid pressure to subatmospheric pressure; and the vacuum control signal can not be taken from the outlet passageway of the valve because the pressure is unstable in the outlet passageway. Since the pressure is unstable in the outlet passageway, a sufficient length of piping must be connected between the outlet passageway and the fluid user to allow the fluid pressure to stabilize if the vacuum control signal is to be taken from the connection between the valve and the fluid user.
Chemical injection systems, such as used in coin operated car washes, are also known in the art. A typical chemical injection system used by coin operated car washes receives its main fluid or water supply from a public water supply. The water supply must be protected from contamination by the chemicals used in the car wash. This is normally accomplished by installing a tank having a level operated float inside the tank and a level transmitter connected to the float. The level transmitter provides a signal to a control valve which is in the water supply. The float and level transmitter operate the control valve to maintain a level of water in the tank. The water dumps into the tank at a point above the normal level of water in the tank to prevent any back flow of water from the tank into the water supply. The tank is connected to a pump which supplies the high pressure water to the car wash. In order to inject chemicals, such as soap and wax, into the car wash a flow restriction orifice is placed in the line between the pump and the float tank in order to create a vacuum between the pump and the flow restriction orifice. A chemical supply is connected between the pump and the orifice and the vacuum created between the pump and the orifice draws chemicals from the chemical supply into the pump and car wash. A shortcoming of this type of chemical injection system is its relative complexity, maintenance cost, and installation cost.